Do NOT buy trooper crates! These are by far the worst value. Always buy hero crates. I suppose if your main game is starfighter assault, those crates aren't too badly priced either. But the trooper crates are horrible value! It's a bit off to complain "the progression is way too slow!" when you're gimping yourself to ~55% progress through choosing the slowest option every time. Even if you're playing troopers at all times, hero crates are a much better value!
Don't think of crates as a means to get cards! They are a means to get crafting mats, which are a means to get exactly the card you want. As far as I know every regular crate (Trooper / Starfighter / Hero) has a guaranteed drop of 35-50 crafting mats. On average easily enough for a new rank1 star card. Think of each hero crate akin to a "skill point" in any regular game, it unlocks 1 ability of your choice. The rest of the stuff it gives are secondary, unlikely to be what you want (but doesn't matter, since you are guaranteed what you want!). You will of course pick up a lot of cards along the way anyhow, which saves some crafting mats.
Strongly consider buying hero crates instead of unlocking heroes at the start. If you must have Darth Vader, or if your main game is HvV then I suppose fair enough. To the general galactic assault beginner player though, chances are it's a pretty rare to score enough BP in a game with zero-card classes to even make use of the most expensive heroes. So I think at the least using hero crates (the crafting mats from them) to unlock the 2nd star card slot for your regular class(es), and add some basic buffs / abilities you like the look of is a good idea. And then when you do get to unlocking the remaining heroes, you have the majority of their cards unlocked already.
If you use this hero crate strat, duplicates are not (as much of) a useless waste (as they are in trooper crates), since the price of a hero crate is so much cheaper. Every 11 dupes are a free hero crate, or equivalently another ~40 crafting mats (the real currency). Because the pool of hero cards is quite small,
Saving all credits for an eventual unknown rebalance seems like a terrible idea to me. I consider it far more likely a rebalance will alter credit earn rate, rather than let that remain constant and tweak the prices of things and risk the ire of people who have spent credits already.
edit:
I don't mean to call you out, I realize trooper crates are the top of the list and the default choice. But this is a perfect example. You've been spending twice as much credits as you needed to, no wonder it feels they are infrequent and not worth it. But you can "double credit payout" for yourself whenever you want - choose hero crates, craft the cards you want :)
